When you copy and paste on a Mac, you usually get the style along with the text you are pasting. This is annoying in things like email, you copy a previous response and it has the format of previous response and even worse, sometimes that format change affects the rest of the text you type. If you want to copy the text, but not the style, you can do this using a different shortcut for the pasting. Copy as usual using Command + C. But when you paste, instead of just using Command + V, use Command + Shift + Option + V. When you do the paste in this way, the text will be pasted, but the formatting will not.